Amiga Halfbrite mode

Extra Half-Brite (EHB) mode is a planar display mode of the Commodore Amiga computer. It uses six bitplanes (six bits/pixel). The first five bitplanes index 32 colors selected from a 12-bit color space (4096 possible colors). If the bit on the sixth bitplane is set the display hardware halves the brightness of the corresponding color component. This way 64 simultaneous colors are possible (32 arbitrary colors plus 32 half-bright components) while only using 32 color registers. The number of color registers is a hardware limitation of pre-AGA chipsets used in Amiga computers.